U.S. patent application number 13/689115 was filed with the patent office on 2013-10-17 for fixing device and image forming apparatus.
This patent application is currently assigned to FUJI XEROX CO., LTD.. The applicant listed for this patent is FUJI XEROX CO., LTD.. Invention is credited to Yoshihiro HAYASHI, Toshiyuki MIYATA, Yasuto OKABAYASHI.
Application Number | 20130272758 13/689115 |
Document ID | / |
Family ID | 49325212 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130272758 |
Kind Code |
A1 |
HAYASHI; Yoshihiro ; et
al. |
October 17, 2013 |
FIXING DEVICE AND IMAGE FORMING APPARATUS
Abstract
A fixing device includes a heating member heating a recording
medium to fix a developer image thereto; an endless heating belt
rotatably wrapped around the heating member and heating the medium;
a rotating member around which the belt is wrapped and having a
fixed first axial end; a position detecting unit detecting a
position of the belt when moved in first and second opposite
directions parallel to an axial direction of the rotating member;
and a controller controlling a rotational movement angle by which a
second axial end of the rotating member is rotationally moved about
the first end in an axis-intersecting direction based on
information from the position detecting unit when the belt is moved
in the first and second directions so that first and second speeds
for respectively moving the belt in the first and second directions
are made equal to or close to each other.
Inventors: |
HAYASHI; Yoshihiro;
(Kanagawa, JP) ; OKABAYASHI; Yasuto; (Kanagawa,
JP) ; MIYATA; Toshiyuki; (Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI XEROX CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
49325212 |
Appl. No.: |
13/689115 |
Filed: |
November 29, 2012 |
Current U.S.
Class: |
399/329 |
Current CPC
Class: |
G03G 15/2053 20130101;
G03G 2215/00156 20130101; G03G 15/2017 20130101; G03G 2215/2032
20130101; G03G 2215/2038 20130101 |
Class at
Publication: |
399/329 |
International
Class: |
G03G 15/20 20060101
G03G015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2012 |
JP |
2012-090920 |
Claims
1. A fixing device comprising: a heating member that heats a
recording medium so as to fix an unfixed developer image
transferred on the recording medium onto the recording medium; an
endless heating belt that is wrapped around the heating member in a
rotatable manner in a circumferential direction of the endless
heating belt and heats the recording medium; a rotating member
around which the endless heating belt is wrapped and that is
provided in a rotatable manner in a state where a first axial end
of the rotating member is fixed; a position detecting unit that
detects a position of the endless heating belt when the endless
heating belt is moved in a first direction and a second direction,
which are opposite to each other and extend parallel to an axial
direction of the rotating member; and a controller that controls a
rotational movement angle by which a second axial end of the
rotating member is rotationally moved about the first axial end of
the rotating member in a direction intersecting the axial direction
on the basis of information from the position detecting unit when
the endless heating belt is moved in the first direction and the
second direction so that a first speed at which the endless heating
belt is moved in the first direction is made equal to or close to a
second speed at which the endless heating belt is moved in the
second direction.
2. The fixing device according to claim 1, wherein the controller
performs control for changing a distance by which the endless
heating belt is moved in the first direction and the second
direction in accordance with a type of the recording medium or a
traveling speed of the recording medium in the fixing device.
3. The fixing device according to claim 1, wherein the controller
stores the rotational movement angle for the rotating member in
accordance with a state of a fixing process and performs control by
using the stored rotational movement angle as an initial preset
value when switching the state of the fixing process.
4. An image forming apparatus comprising: an image bearing member
that bears a developer image; a transfer unit that transfers the
developer image on the image bearing member onto a recording
medium; and the fixing device according to claim 1 that fixes the
developer image in an unfixed state transferred on the recording
medium onto the recording medium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2012-090920 filed Apr.
12, 2012.
BACKGROUND
Technical Field
[0002] The present invention relates to fixing devices and image
forming apparatuses.
SUMMARY
[0003] According to an aspect of the invention, there is provided a
fixing device including a heating member, an endless heating belt,
a rotating member around which the endless heating belt is wrapped,
a position detecting unit, and a controller. The heating member
heats a recording medium so as to fix an unfixed developer image
transferred on the recording medium onto the recording medium. The
endless heating belt is wrapped around the heating member in a
rotatable manner in a circumferential direction of the endless
heating belt and heats the recording medium. The rotating member is
provided in a rotatable manner in a state where a first axial end
thereof is fixed. The position detecting unit detects a position of
the endless heating belt when the endless heating belt is moved in
a first direction and a second direction, which are opposite to
each other and extend parallel to an axial direction of the
rotating member. The controller controls a rotational movement
angle by which a second axial end of the rotating member is
rotationally moved about the first axial end of the rotating member
in a direction intersecting the axial direction on the basis of
information from the position detecting unit when the endless
heating belt is moved in the first direction and the second
direction so that a first speed at which the endless heating belt
is moved in the first direction is made equal to or close to a
second speed at which the endless heating belt is moved in the
second direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Exemplary embodiments of the present invention will be
described in detail based on the following figures, wherein:
[0005] FIG. 1 schematically illustrates an image forming apparatus
according to a first exemplary embodiment of the present
invention;
[0006] FIG. 2 schematically illustrates an example of a fixing
device in the image forming apparatus in FIG. 1;
[0007] FIG. 3 is a plan view of a heating belt and an internal
heating roller when the fixing device in FIG. 2 is viewed from
above;
[0008] FIGS. 4A and 4B schematically illustrate an example of a
position detector that detects the position of the heating belt of
the fixing device in FIG. 2;
[0009] FIG. 5 is a circuit block diagram illustrating an example
related to control of reciprocation of the heating belt in the
fixing device shown in FIG. 2;
[0010] FIG. 6 illustrates an example of control of the
reciprocation of the heating belt during operation of the fixing
device in FIG. 2; and
[0011] FIG. 7 schematically illustrates an example of a fixing
device in an image forming apparatus according to a second
exemplary embodiment of the present invention.
DETAILED DESCRIPTION
[0012] Exemplary embodiments of the present invention will be
described in detail below with reference to the drawings. In the
drawings used for explaining the exemplary embodiments, the same
components will basically be given the same reference numerals, and
redundant descriptions thereof will be omitted.
First Exemplary Embodiment
[0013] FIG. 1 schematically illustrates an image forming apparatus
1 according to a first exemplary embodiment of the present
invention.
[0014] The image forming apparatus 1 according to this exemplary
embodiment is, for example, a tandem-type color printer and
includes multiple image forming units 20, an intermediate transfer
belt 30 as an example of an image bearing member, a backup roller
41 and a second-transfer roller 42 as an example of a transfer
unit, sheet feed trays 50a and 50b, a sheet transport system 60,
and a fixing device 70.
[0015] The image forming units 20 include four color image forming
units 20Y, 20M, 20C, and 20K that respectively form, for example,
yellow, magenta, cyan, and black toner images, and two
transparent-color image forming units 20CL that transfer, for
example, transparent-color toner images. The image forming units 20
first-transfer the toner images formed in accordance with image
information for the respective colors onto the intermediate
transfer belt 30.
[0016] In the rotational direction of the intermediate transfer
belt 30, the six image forming units 20CL, 20Y, 20M, 20C, and 20K
are arranged in the following order: transparent color, transparent
color, yellow, magenta, cyan, and black. Alternatively, light-color
image forming units that transfer light-color toner images, such as
light yellow, light magenta, light cyan, or light black toner
images, may be provided in place of the transparent-color image
forming units 20CL. As another alternative, a transparent-color
image forming unit 20CL and a light-color image forming unit may
both be provided.
[0017] Each of the image forming units 20 includes a photoconductor
drum 21, a charging device 22 that electrostatically charges the
surface of the photoconductor drum 21 to a predetermined electric
potential, an exposure device 23 that radiates laser light L onto
the electrostatically-charged photoconductor drum 21 so as to form
an electrostatic latent image thereon, a developing device 24 that
forms a developer image by developing the electrostatic latent
image formed on the photoconductor drum 21, a first-transfer roller
25 that transfers the developer image on the photoconductor drum 21
onto the intermediate transfer belt 30 at a first-transfer area,
and a drum cleaner 26 that removes residual toner and paper
particles from the surface of the photoconductor drum 21 after the
developer image is transferred therefrom. A toner cartridge 27 that
supplies a developer to the developing device 24 is disposed above
the image forming unit 20.
[0018] In each image forming unit 20, the first-transfer roller 25
is disposed facing the photoconductor drum 21 with the intermediate
transfer belt 30 interposed therebetween. When a transfer bias
voltage with reversed polarity relative to the charge polarity of
the toner is applied to the first-transfer roller 25, an electric
field is generated between the photoconductor drum 21 and the
first-transfer roller 25, so that the electrically-charged
developer image on the photoconductor drum 21 is transferred onto
the intermediate transfer belt 30 due to Coulomb force. The
photoconductor drum 21 rotates clockwise for the first-transfer
process.
[0019] The intermediate transfer belt 30 is a component to which
the developer images of the respective color components formed by
the image forming units 20 are sequentially transferred
(first-transferred). The intermediate transfer belt 30 is an
endless belt wrapped around multiple support rollers 31a to 31f and
the backup roller 41. The intermediate transfer belt 30 rotates
counterclockwise in the circumferential direction thereof while the
developer images formed on the image forming units 20CL, 20Y, 20M,
20C, and 20K are first-transferred thereto.
[0020] The backup roller 41 and the second-transfer roller 42
forming a pair serve as a mechanism for forming a full-color image
by collectively transferring the developer images superposed and
transferred on the intermediate transfer belt 30 onto a sheet (as
an example of a recording medium), and are disposed facing each
other with the intermediate transfer belt 30 interposed
therebetween. An area where the backup roller 41 and the
second-transfer roller 42 face each other is a second-transfer
area.
[0021] The backup roller 41 is rotatably disposed at the reverse
side of the intermediate transfer belt 30, whereas the
second-transfer roller 42 is rotatably disposed facing the
developer-image transfer face of the intermediate transfer belt 30.
The backup roller 41 and the second-transfer roller 42 are disposed
such that the rotation axes thereof extending orthogonally to the
plane of FIG. 1 are parallel to each other.
[0022] When transferring the developer images onto the intermediate
transfer belt 30, a voltage with the same polarity as the charge
polarity of the toners is applied to the backup roller 41, or a
voltage with reversed polarity relative to the charge polarity of
the toners is applied to the second-transfer roller 42. Thus, a
transfer electric field is generated between the backup roller 41
and the second-transfer roller 42, whereby unfixed developer images
on the intermediate transfer belt 30 are transferred onto the
sheet.
[0023] The sheet feed trays 50a and 50b accommodate sheets of
various sizes and thicknesses. A sheet in one of the sheet feed
trays 50a and 50b is fetched by a pickup roller (not shown) of the
sheet transport system 60 and is subsequently timing-controlled by
a registration roller 62 of the sheet transport system 60 so as to
be introduced to the second-transfer area, where the developer
images are transferred onto the sheet. Then, the sheet is
transported to the fixing device 70 via transport belts 63 and 64
of the sheet transport system 60.
[0024] The fixing device 70 fixes the unfixed developer images
transferred on the sheet at the second-transfer area onto the sheet
by thermo-compression, and includes a heating roller 71 as an
example of a heating member, a pressing roller 72 disposed facing
the heating roller 71, and a heating belt 73 moving through a
fixation nip N formed between the heating roller 71 and the
pressing roller 72.
[0025] After the second-transfer process, the sheet is transported
to the fixation nip N and is output therefrom while being nipped
between the heating belt 73 and the pressing roller 72. In this
case, the sheet is heated by the heating roller 71 and the heating
belt 73 and is pressed by the pressing roller 72, whereby the
developer images are fixed onto the sheet. The sheet traveling
through the fixing device 70 is transported to an output roller
(not shown) via a transport belt 65 and is output outward from the
image forming apparatus 1.
[0026] FIG. 2 schematically illustrates an example of the fixing
device 70 shown in FIG. 1.
[0027] In addition to the heating roller 71, the pressing roller
72, and the heating belt 73 described above, the fixing device 70
includes a separating pad 74, an internal heating roller 75 as an
example of a rotating member, an external heating roller 76,
support rollers 77a and 77b, and a cooling fan 78.
[0028] The heating roller 71 heats a sheet P and the heating belt
73. The heating roller 71 is a cylindrical roller composed of a
metallic material, such as aluminum, iron, or stainless steel, and
has three heating sources 71L, such as halogen lamps, disposed
therein.
[0029] Alternatively, the number of heating sources 71L may be two
or smaller, or may be four or greater. Furthermore, multiple
heating sources 71L with different calorific values may be disposed
such that optimal temperature distribution is generated in
accordance with the size of the sheet P, and these heating sources
71L may be selectively used in accordance with the size of the
sheet P. Moreover, if the temperature differs between the center
and the edges of the sheet P in the width direction (i.e., a
direction orthogonal to the plane of FIG. 2) thereof, the heating
sources 71L may be disposed in correspondence with the center and
the edges of the sheet P in the width direction thereof so that the
in-plane temperature of the sheet P is made uniform.
[0030] The heating roller 71 serves as a driving source for
rotationally driving the pressing roller 72 and the heating belt
73, and is rotatable in a counterclockwise direction R1 by
receiving a driving force from a rotational driving motor (not
shown). When the heating roller 71 rotates, the sheet P is
transported, and the pressing roller 72 and the heating belt 73 are
rotated (slave-driven). A first fixation nip N1 is formed between
the heating roller 71 and the pressing roller 72.
[0031] The separating pad 74 is disposed beside the heating roller
71 (i.e., at the downstream side thereof in the transport direction
of the sheet P) such that the separating pad 74 is adjacent to the
entire axial region of the heating roller 71. The separating pad 74
has a function of separating the sheet P from the heating belt 73
after the fixing process. A second fixation nip N2 is formed
between the separating pad 74 and the pressing roller 72.
Specifically, the fixation nip N in the fixing device 70 includes
the first fixation nip N1 and the second fixation nip N2, and the
fixation nip N is made longer as compared with a case where the
separating pad 74 is not provided.
[0032] Oil is applied between the heating roller 71 and the heating
belt 73, and also between the separating pad 74 and the heating
belt 73. Thus, the contact resistance between the heating roller 71
and the heating belt 73 and the contact resistance between the
separating pad 74 and the heating belt 73 are reduced, thereby
allowing for smooth rotation of the heating belt 73. In addition,
damage to the heating belt 73 caused by the heating roller 71 and
the separating pad 74 coming into contact with each other and the
separating pad 74 and the heating belt 73 coming into contact with
each other may be suppressed or prevented.
[0033] The pressing roller 72 includes a hollow cylindrical cored
bar 72A, an elastic layer 72B covering the outer periphery thereof,
and a mold-release layer 72C covering the outer periphery of the
elastic layer 72B. The cored bar 72A is composed of a metallic
material, such as aluminum, iron, or stainless steel. The elastic
layer 72B is composed of a heat-resistant insulating material, such
as silicone rubber. The mold-release layer 72C is composed of, for
example, a fluorine-based resin material.
[0034] The pressing roller 72 is disposed in a movable manner
toward and away from the heating roller 71 and is pressed against
the heating roller 71 by an elastic member (such as a spring)
during the fixing process. Thus, the first and second fixation nips
N1 and N2 described above are formed between the heating roller 71
and the pressing roller 72 and between the separating pad 74 and
the pressing roller 72, respectively.
[0035] The heating belt 73 is an endless belt formed by laminating
a mold-release layer composed of, for example, fluorine-based resin
over a heat-resistant insulating material, such as polyimide resin.
The heating belt 73 is wrapped around the heating roller 71, the
internal heating roller 75, and the support rollers 77a and 77b and
is rotatable in the circumferential direction (i.e., a
counterclockwise direction R2).
[0036] The heating belt 73 is wrapped so as to travel through the
first and second fixation nips N1 and N2. The sheet P transported
to the first and second fixation nips N1 and N2 is heated by the
heating roller 71 and the heating belt 73 while being nipped
between the heating belt 73 and the pressing roller 72, and is also
pressed by the pressing roller 72. Thus, the unfixed developer
images on the sheet P become fixed onto the sheet P. The surface of
the sheet P on which the developer images are formed is made to
come into contact with the outer peripheral surface (i.e., the
mold-release layer) of the heating belt 73.
[0037] If the sheet P is to be heated with the heating roller 71
alone without using the heating belt 73, the heat from the heating
roller 71 would be absorbed by the sheet P during the fixing
process, thus causing the heating temperature of the heating roller
71 to decrease. Since it takes time to increase the temperature to
a sufficient value due to the heating roller 71 having a large heat
capacity, the temperature for heating a subsequent sheet P during
the fixing process therefor decreases.
[0038] In contrast, when the heating belt 73 is used, the
temperature of the heating belt 73 is quickly increased to a
sufficient value due to having a smaller heat capacity than the
heating roller 71. Therefore, a decrease in the temperature for
heating the subsequent sheet P during the fixing process therefor
may be suppressed. Furthermore, when the heating belt 73 is used,
the length thereof is made longer than the length of the sheet P in
the transport direction thereof so that the temperature for heating
the sheet P is made uniform over the entire area thereof in the
transport direction, thereby suppressing or preventing uneven
glossiness.
[0039] The internal heating roller 75 is disposed farther away from
the pressing roller 72 than the heating roller 71 and the external
heating roller 76 are from the pressing roller 72, and is rotatable
by being slave-driven by the rotation of the heating belt 73.
[0040] The internal heating roller 75 is a cylindrical roller
composed of a metallic material, such as aluminum, iron, or
stainless steel, and has four heating sources 75L, such as halogen
lamps, disposed therein for heating the heating belt 73 from the
inner peripheral surface thereof.
[0041] Alternatively, the number of heating sources 75L may be
three or smaller, or may be five or greater. Furthermore, multiple
heating sources 75L with different calorific values may be disposed
such that optimal temperature distribution is generated in
accordance with the size of the sheet P, and these heating sources
75L may be selectively used in accordance with the size of the
sheet P. Moreover, if the temperature differs between the center
and the edges of the sheet P in the width direction (i.e., the
direction orthogonal to the plane of FIG. 2) thereof, the heating
sources 75L may be disposed in correspondence with the center and
the edges of the sheet P in the width direction thereof so that the
in-plane temperature of the sheet P is made uniform.
[0042] As another alternative, a rotating roller as an example of a
rotating unit not provided with the heating sources 75L may be
disposed at this position in place of the internal heating roller
75. This rotating roller only differs from the internal heating
roller 75 in that the heating sources 75L are not provided, but is
the same as the internal heating roller 75 with respect to the
remaining configuration including a configuration to be described
later.
[0043] The external heating roller 76 heats the heating belt 73
from the outer peripheral surface thereof and is disposed between
the heating roller 71 and the internal heating roller 75. The
external heating roller 76 is disposed in contact with the outside
of the heating belt 73 so as to press the heating belt 73 toward
the inside thereof, and is rotatable by being slave-driven by the
rotation of the heating belt 73.
[0044] The external heating roller 76 is a cylindrical roller
composed of a metallic material, such as aluminum, iron, or
stainless steel, and has three heating sources 76L, such as halogen
lamps, disposed therein.
[0045] Alternatively, the number of heating sources 76L may be two
or smaller, or may be four or greater. Furthermore, multiple
heating sources 76L with different calorific values may be disposed
such that optimal temperature distribution is generated in
accordance with the size of the sheet P, and these heating sources
76L may be selectively used in accordance with the size of the
sheet P. Moreover, if the temperature differs between the center
and the edges of the sheet P in the width direction (i.e., the
direction orthogonal to the plane of FIG. 2) thereof, the heating
sources 76L may be disposed in correspondence with the center and
the edges of the sheet P in the width direction thereof so that the
in-plane temperature of the sheet P is made uniform.
[0046] In the fixing device 70 described above, the unfixed
developer images on the surface of the sheet P transported to the
fixation nip N are fixed onto the sheet P by heat and pressure
applied to the first fixation nip N1.
[0047] The heat applied to the first fixation nip N1 is supplied to
the sheet P by the heating belt 73. Specifically, at the first
fixation nip N1, heat energy is supplied to the sheet P from the
heating belt 73 heated by the three heating rollers, i.e., the
heating roller 71, the internal heating roller 75, and the external
heating roller 76, whereby a sufficient amount of heat is ensured
even in a high-speed process.
[0048] Furthermore, because the heating belt 73 has an extremely
small heat capacity relative to the heating roller 71 and the like,
and is in contact with the three heating rollers 71, 75, and 76
with wide wrap areas (i.e., large wrap angles), the heating belt 73
receives a sufficient amount of heat from the three heating rollers
71, 75, and 76 within a short period in which the heating belt 73
makes one rotation. Therefore, the temperature of the heating belt
73 returns to a sufficient fixation temperature within a short
period of time, so that a predetermined fixation temperature is
maintained at the first fixation nip N1.
[0049] Consequently, a sufficient fixation temperature is
maintained in the fixing device 70 even when multiple sheets are
successively fed at high speed. In addition, a so-called
temperature droop phenomenon in which the fixation temperature
drops when commencing a fixing process at high speed may be
suppressed. In particular, the fixation temperature is maintained
and the temperature droop phenomenon is suppressed even when a
thick sheet of paper having a large heat capacity is used. In
addition, even if the fixation temperature is to be increased or
decreased in the middle of the process in accordance with the type
of sheet used, because the heating belt 73 has a small heat
capacity, the fixation temperature may be readily changed by
adjusting the outputs from the heating sources 71L, 75L, and
76L.
[0050] Furthermore, because the heating roller 71 is composed of
aluminum or the like, and the pressing roller 72 has the elastic
layer, the surface of the pressing roller 72 bends at the first
fixation nip N1 whereas the heating roller 71 hardly bends, whereby
a fixation nip with a sufficient width in the moving direction of
the heating belt 73 is formed. Therefore, at the first fixation nip
N1, the side of the heating roller 71 around which the heating belt
73 is wrapped hardly deforms, so that the heating belt 73 passes
through the first fixation nip N1 while the moving speed thereof is
maintained at a preset speed. Consequently, the occurrence of
wrinkling or distortion of the heating belt 73 at the first
fixation nip N1 may be suppressed, whereby a high-quality, stable
fixed image may be obtained.
[0051] The first fixation nip N1 has a shape of a
downwardly-protruding curve due to the curvature of the heating
roller 71, whereas the second fixation nip N2 has a shape of an
upwardly-protruding curve due to the curvature of the pressing
roller 72. Therefore, the traveling direction of the sheet P heated
and pressed at the first fixation nip N1 under the curvature of the
heating roller 71 is changed at the second fixation nip N2 due to
the curvature of the pressing roller 72 oriented in the opposite
direction. In this case, slight micro-slippage occurs between the
developer images on the sheet P and the outer peripheral surface of
the heating belt 73 so that the adhesive force between the
developer images and the heating belt 73 is weakened, whereby the
sheet P becomes readily separable from the heating belt 73.
Accordingly, the second fixation nip N2 is an area corresponding to
a preparation stage for reliably separating the sheet P in the
final separating process.
[0052] At the exit of the second fixation nip N2, the heating belt
73 is transported in a wrapped state around the separating pad 74
so that the transport direction of the heating belt 73 suddenly
changes at the exit. Therefore, the sheet P whose adhesive force
against the heating belt 73 is weakened at the second fixation nip
N2 becomes separated from the heating belt 73 due to the resilience
of the sheet P. The separated sheet P is transported toward a
cooling unit (not shown) via the transport belt 65 and the
like.
[0053] In the belt-type fixing device 70 described above, when
multiple sheets of thick paper or the like are processed, the
heating belt 73 may possibly become damaged when extremely large
pressure is applied to an area thereof that comes into contact with
an edge of thick paper. When such thick paper is replaced with a
large-size sheet of paper, the damaged area may possibly be
reflected on an image on the sheet.
[0054] Hence, the heating belt 73 is reciprocated equally in the
order of millimeters in the axial direction (i.e., longitudinal
direction) of the internal heating roller 75, so that the damage
occurring in the heating belt 73 is distributed. Specifically, when
the same area of the heating belt 73 is repeatedly damaged, the
damaged area becomes larger, leading to greater deterioration in
image quality. In contrast, by reciprocating the heating belt 73 in
the left-right direction, the damaged area is shifted so that the
same area is prevented from being repeatedly damaged, thereby
suppressing or preventing image-quality deterioration caused by a
damaged area in the heating belt 73. In this case, although the
glossiness of the image may be reduced, the lifespan of the fixing
device 70 is extended since image-quality deterioration caused by a
damaged area in the heating belt 73 is suppressed or prevented.
[0055] FIG. 3 is a plan view of the heating belt 73 and the
internal heating roller 75 when the fixing device 70 in FIG. 2 is
viewed from above.
[0056] In this exemplary embodiment, a first axial end 75E1 of the
internal heating roller 75 is fixed to the front surface or the
rear surface of the image forming apparatus 1, whereas a second
axial end 75E2 of the internal heating roller 75 is rotationally
movable by a driver (not shown in FIG. 3), such as a motor, in a
direction R3 (simply referred to as "axis-intersecting direction"
hereinafter) intersecting the axial direction of the internal
heating roller 75.
[0057] By rotationally moving the second end 75E2 of the internal
heating roller 75 in the axis-intersecting direction R3 about the
fixed first end 75E1, the heating belt 73 is reciprocated in the
axial direction, indicated by an arrow X1, of the internal heating
roller 75. The reciprocation of the heating belt 73 is controlled
on the basis of steering angles .theta.1 and .theta.2 (as an
example of rotational movement angles) used when moving the second
end 75E2 of the internal heating roller 75 in the axis-intersecting
direction R3.
[0058] Alternatively, when reciprocating the heating belt 73, both
axial ends of the internal heating roller 75 may be moved in the
direction intersecting the axial direction thereof. In this case,
the two axial ends of the internal heating roller 75 may be moved
symmetrically for reciprocating the heating belt 73. However, in
actuality, it is difficult to control the movement of both axial
ends of the internal heating roller 75, and moreover, drivers, such
as motors, are provided for both axial ends of the internal heating
roller 75, leading to an increase in size and cost of the
device.
[0059] Unlike the above case where both axial ends of the internal
heating roller 75 are operated, this exemplary embodiment achieves
facilitated control by simply operating the second axial end 75E2
and only uses a single driver, such as a motor, thereby achieving
size reduction and cost reduction. However, when one end of the
internal heating roller 75 is fixed, the internal heating roller 75
becomes unsymmetrical for the reciprocation of the heating belt 73,
causing the heating belt 73 to become readily unbalanced toward one
of the axial ends of the internal heating roller 75. In addition,
due to individual differences between fixing devices 70 and changes
occurring in components and materials over time, the
controllability of the aforementioned steering angles .theta.1 and
.theta.2 may deteriorate. Since this may cause variations in the
reciprocation of the heating belt 73, damaged positions along the
widthwise edges of the heating belt 73 may vary, possibly resulting
in uneven glossiness in an image. If the heating belt 73 moves
excessively toward one of the axial ends of the internal heating
roller 75 and abuts on a housing of the image forming apparatus 1,
the heating belt 73 may possibly become abraded or break.
[0060] In light of this, a position detector (not shown in FIG. 3)
that detects the position of the heating belt 73 is provided at
each of or one of the axial ends of the internal heating roller 75
in this exemplary embodiment. Based on information from the
position detector or detectors, the steering angles .theta.1 and
.theta.2 for the internal heating roller 75 are controlled so that
the moving period (speed) in which the reciprocating heating belt
73 moves in a first direction is made equal to or close to the
moving period (speed) in which the reciprocating heating belt 73
moves in a second direction. Thus, damaged positions along the
widthwise edges of the heating belt 73 may be evenly distributed,
and differences in the damaged positions between the widthwise
edges of the heating belt 73 may be eliminated, thereby reducing
uneven glossiness in an image fixed by the fixing device 70.
[0061] In addition, the steering angles .theta.1 and .theta.2 for
the internal heating roller 75 are controlled such that an optimal
time period (speed) in which the moving period (speed) of the
reciprocating heating belt 73 moving in the first direction and the
moving period (speed) of the reciprocating heating belt 73 moving
in the second direction are balanced is achieved. Accordingly, the
heating belt 73 may be prevented from moving excessively, whereby
the heating belt 73 may be prevented from becoming abraded or
breaking by abutting on the housing of the image forming apparatus
1.
[0062] FIGS. 4A and 4B schematically illustrate an example of a
position detector 79 described above as an example of a position
detecting unit that detects the position of the heating belt
73.
[0063] The position detector 79 is disposed at, for example, one
axial end of the internal heating roller 75. Alternatively, the
position detector 79 may be disposed at each of the two axial ends
of the internal heating roller 75. If the position detector 79 is
provided at one end of the internal heating roller 75, size
reduction and cost reduction are achieved, as compared with the
case where the position detectors 79 are provided at both ends. If
the position detectors 79 are provided at both ends, the position
detection accuracy is improved, as compared with the case where the
position detector 79 is provided at one end.
[0064] The position detector 79 includes, for example, three
sensors 79Sa to 79Sc and a single control shaft 79C. The sensors
79Sa to 79Sc are, for example, photo-sensors and respectively
include light emitters 79Sa1 to 79Sc1 that emit detection light DL
and light receivers 79Sa2 to 79Sc2 that receive the detection light
DL.
[0065] The light emitters 79Sa1 to 79Sc1 and the light receivers
79Sa2 to 79Sc2 forming pairs are arranged in the axial direction of
the internal heating roller 75 and respectively face each other so
as to emit and receive the detection light DL.
[0066] The light receivers 79Sa2 to 79Sc2 are electrically
connected to a central processing unit (CPU), to be described
later, and each convert the detection light DL into an electric
signal and transmit the electric signal to the CPU.
[0067] A first axial end of the control shaft 79C is pressed
against the corresponding widthwise edge of the heating belt 73 by
an elastic member, such as a spring, whereas a second axial end of
the control shaft 79C is disposed in a movable manner in the axial
direction thereof indicated by an arrow X2 between the light
emitters 79Sa1 to 79Sc1 and the light receivers 79Sa2 to 79Sc2.
[0068] The second end of the control shaft 79C is integrally
provided with a light blocking portion 79Ca that blocks the
detection light DL. When the heating belt 73 reciprocates, the
control shaft 79C moves correspondingly in the direction of the
arrow X2 so that the position of the light blocking portion 79Ca
changes, whereby the position of the heating belt 73 is detected.
For example, the aforementioned CPU is defined such that, when the
detection light DL is blocked by the light blocking portion 79Ca,
the CPU detects an "ON" state. For illustrative purposes, FIG. 4B
shows the light receiver 79Sb2 in the middle as viewed through the
light blocking portion 79Ca.
[0069] FIG. 5 is a circuit block diagram illustrating an example
related to control of the reciprocation of the heating belt 73 in
the fixing device 70 shown in FIG. 2.
[0070] The CPU as an example of a controller controls image
processing in the image forming apparatus 1. The CPU is
electrically connected to a memory ME, and is also electrically
connected to the light receivers 79Sa2 to 79Sc2 of the
aforementioned sensors 79Sa to 79Sc and to a driver 75M that
rotationally moves the second end 75E2 of the internal heating
roller 75 in the axis-intersecting direction R3.
[0071] In the operation of the fixing device 70, detection signals
obtained by the light receivers 79Sa2 to 79Sc2 of the sensors 79Sa
to 79Sc are transmitted to the CPU. The CPU ascertains the position
of the heating belt 73 on the basis of the detection signals and
controls the operation of the driver 75M (i.e., the steering angles
.theta.1 and .theta.2) so that the moving period (speed) in which
the reciprocating heating belt 73 moves in the first direction is
made equal to or close to the moving period (speed) in which the
reciprocating heating belt 73 moves in the second direction.
Accordingly, uneven glossiness in an image fixed by the fixing
device 70 may be reduced.
[0072] In addition, the operation of the driver 75M (i.e., the
steering angles .theta.1 and .theta.2) is controlled such that an
optimal time period (speed) in which the moving period (speed) of
the reciprocating heating belt 73 moving in the first direction and
the moving period (speed) of the reciprocating heating belt 73
moving in the second direction are balanced is achieved.
Accordingly, the heating belt 73 may be prevented from becoming
abraded or breaking.
[0073] Furthermore, the steering angles .theta.1 and .theta.2 for
the internal heating roller 75 are preliminarily stored in the
memory ME in accordance with the state of the fixing process, such
as the state of the fixing device 70 (e.g., the latched state
between the heating roller 71 and the pressing roller 72) or the
traveling state (e.g., the quality or the basis weight of the sheet
P), and are used as initial preset values for the steering angles
.theta.1 and .theta.2 when switching the state. Accordingly, the
time period for performing initial setting related to the
reciprocation of the endless heating belt 73 when switching the
state of the fixing process may be shortened.
[0074] Furthermore, a maximum moving distance for the reciprocation
of the heating belt 73 may be changed in the fixing device 70 in
accordance with the type of sheet P used (such as the thickness or
the material thereof). For example, if a thin sheet of paper is
used, since the sheet has a small heat capacity and the rotation
speed of the heating belt 73 is high from a standpoint of a
high-speed process, the turn-around points of the reciprocating
heating belt 73 are detected early so as to prevent the edges of
the heating belt 73 from moving excessively. When a thick sheet of
paper is used, since the sheet has a large heat capacity, the
rotation speed of the heating belt 73 is reduced relative to that
for a thin sheet of paper so as to sufficiently heat the thick
sheet. In addition, the thick sheet may cause greater damage to the
heating belt 73. In view of these factors, it is better to increase
the distance for the reciprocation of the heating belt 73 so that
the damaged positions can be distributed, thus reducing
deterioration in image quality caused by the damaged positions.
Therefore, for example, when performing a fixing process on a thick
sheet of paper, the distance for the reciprocation of the heating
belt 73 is increased relative to that for a thin sheet of paper.
Accordingly, even when a thick sheet of paper that tends to form
scratches on the heating belt 73 is used, the heating belt 73
reciprocates by an increased distance so that the damaged positions
may be further distributed, thereby suppressing image-quality
deterioration and reducing uneven glossiness in an image.
[0075] However, even in the same sheet P, the sheet P is sometimes
made to travel at different traveling speeds. Therefore, the
maximum moving distance for the reciprocation of the heating belt
73 may be changed in the fixing device 70 in accordance with the
traveling speed of the sheet P. For example, when the sheet P
travels at low speed, the moving distance for the reciprocation of
the heating belt 73 is increased. Accordingly, the heating belt 73
reciprocates by a larger distance so that the damaged positions may
be further distributed, thereby suppressing image-quality
deterioration and reducing uneven glossiness in an image.
[0076] Next, an example of control of the reciprocation of the
heating belt 73 during the fixing process will be described below
with reference to FIGS. 3 to 6. For illustrative purposes, FIG. 6
shows the light receivers 79Sa2 to 79Sc2 as viewed through the
light blocking portion 79Ca.
[0077] The first row in FIG. 6 shows relevant detection components
of the position detector 79 when the heating belt 73 is positioned
at the center of the internal heating roller 75 in the axial
direction thereof. At this stage, the light blocking portion 79Ca
of the control shaft 79C only blocks the detection light DL
entering the light receiver 79Sb2 of the middle sensor 79Sb. In
this case, the detection states of the sensors 79Sa to 79Sc are
"off", "on", and "off" in that order from the left.
[0078] Subsequently, when the heating belt 73 is moved in the axial
direction of the internal heating roller 75 toward the front
surface of the image forming apparatus 1 from the state shown in
the first row, the light blocking portion 79Ca of the control shaft
79C pressed by the corresponding edge of the heating belt 73 is
positioned to block the detection light DL entering the light
receivers 79Sb2 and 79Sc2 of the two sensors 79Sb and 79Sc at the
right side, as shown in the second row in FIG. 6. In this case, the
detection states of the sensors 79Sa to 79Sc are "off", "on", and
"on" in that order from the left. Then, the CPU determines that the
heating belt 73 has reached the turn-around point near the second
axial end 75E2 of the internal heating roller 75 and causes the
driver 75M to move the second axial end 75E2 of the internal
heating roller 75 by predetermined steering angles .theta.1 and
.theta.2 in the axis-intersecting direction R3 so that the heating
belt 73 is moved in the opposite direction toward the rear surface
of the image forming apparatus 1.
[0079] Subsequently, when the heating belt 73 is moved toward the
center from the second axial end 75E2 of the internal heating
roller 75, the control shaft 79C also moves so that the light
blocking portion 79Ca of the control shaft 79C is positioned to
block the detection light DL entering the light receiver 79Sb2 of
the middle sensor 79Sb, as shown in the third row in FIG. 6. In
this case, the detection states of the sensors 79Sa to 79Sc are
"off", "on", and "off" in that order from the left.
[0080] Subsequently, when the heating belt 73 is moved toward the
first axial end 75E1 of the internal heating roller 75 from the
center thereof, the control shaft 79C also moves so that the light
blocking portion 79Ca is positioned to block the detection light DL
entering the light receivers 79Sa2 and 79Sb2 of the sensors 79Sa
and 79Sb, as shown in the fourth row in FIG. 6. In this case, the
detection states of the sensors 79Sa to 79Sc are "on", "on", and
"off" in that order from the left. Then, the CPU determines that
the heating belt 73 has reached the turn-around point near the
first axial end 75E1 of the internal heating roller 75 and causes
the driver 75M to move the second axial end 75E2 of the internal
heating roller 75 by predetermined steering angles .theta.1 and
.theta.2 in the axis-intersecting direction R3 so that the heating
belt 73 is moved in the opposite direction toward the front surface
of the image forming apparatus 1.
[0081] When reciprocating the heating belt 73 in this manner in
this exemplary embodiment, the steering angles .theta.1 and
.theta.2 for the internal heating roller 75 are controlled so that
the time period (speed) in which the heating belt 73 moves from the
front surface toward the rear surface of the image forming
apparatus 1 and the time period (speed) in which the heating belt
73 moves from the rear surface toward the front surface are made
equal to or close to each other. Accordingly, damaged positions
along the widthwise edges of the heating belt 73 may be evenly
distributed, and differences in the damaged positions between the
widthwise edges of the heating belt 73 may be eliminated, thereby
reducing uneven glossiness in an image fixed by the fixing device
70.
[0082] Furthermore, the steering angles .theta.1 and .theta.2 for
the internal heating roller 75 are controlled such that an optimal
period (speed) in which the moving period (speed) of the heating
belt 73 moving from the front surface toward the rear surface of
the image forming apparatus 1 and the moving period (speed) of the
heating belt 73 moving from the rear surface toward the front
surface are balanced is achieved. Accordingly, the heating belt 73
may be prevented from moving excessively, whereby the heating belt
73 may be prevented from becoming abraded or breaking.
[0083] Furthermore, the steering angles .theta.1 and .theta.2 for
the internal heating roller 75 are preliminarily stored in the
memory ME in accordance with the state of the fixing process, such
as the state of the fixing device 70 (e.g., the latched state
between the heating roller 71 and the pressing roller 72) or the
traveling state (e.g., the quality or the basis weight of the sheet
P), and are used as initial preset values for the steering angles
.theta.1 and .theta.2 when switching the state. Accordingly, the
time period for performing initial setting related to the
reciprocation of the endless heating belt 73 when switching the
state of the fixing process may be shortened.
[0084] Furthermore, the maximum moving distance for the
reciprocation of the heating belt 73 may be changed in accordance
with the type of sheet P used (such as the thickness or the
material thereof) or the traveling speed of the sheet P. For
example, when performing a fixing process on a thick sheet of
paper, the distance for the reciprocation of the heating belt 73 is
increased relative to that for a thin sheet of paper. Accordingly,
even when a thick sheet of paper that tends to form scratches on
the heating belt 73 is used, the heating belt 73 reciprocates by an
increased distance so that the damaged positions may be further
distributed, thereby suppressing image-quality deterioration and
reducing uneven glossiness in an image.
[0085] In order to increase the distance for the reciprocation of
the heating belt 73 when performing a fixing process on a thick
sheet of paper, the turn-around points of the heating belt 73 may
be changed. For example, in the above example, it is determined
that the heating belt 73 has reached one of the turn-around points
of the reciprocation when the detection states of the sensors 79Sa
to 79Sc are "off", "on", and "on", or "on", "on", and "off", as
shown in the second row or the fourth row in FIG. 6. Alternatively,
it may be determined that the heating belt 73 has reached one of
the turn-around points of the reciprocation when the outermost
sensor 79Sa or 79Sc is in the "on" state, such as when the
detection states of the sensors 79Sa to 79Sc are "off", "off", and
"on", or "on", "off", and "off".
[0086] As another example, the position detector 79 may include,
for example, four sensors. In this case, when the sheet P is a thin
sheet of paper, one of the outermost sensors may be disabled by
being turned off. When the sheet P is changed to a thick sheet of
paper, the outermost sensor may be enabled so that when the
outermost sensor is detected as being in the "on" state, the
reciprocating heating belt 73 may be determined that it has reached
the corresponding turn-around point. Alternatively, the number of
sensors in the position detector 79 may be four or more.
Second Exemplary Embodiment
[0087] FIG. 7 schematically illustrates a fixing device 70 in an
image forming apparatus 1 according to a second exemplary
embodiment of the present invention.
[0088] In the fixing device 70 according to this exemplary
embodiment, a heating pad 71p is provided in place of the heating
roller 71 and the separating pad 74 described above. The fixation
nip N is formed between the heating pad 71p and the pressing roller
72. In this case, image misalignment may be suppressed or prevented
since the fixation nip N has no inflection points. Therefore, image
defects may be suppressed or prevented.
[0089] The heating pad 71p heats the sheet P and the heating belt
73. The heating pad 71p is formed of a tubular member composed of,
for example, aluminum, iron, or stainless steel. A surface of the
heating pad 71p that is in contact with the heating belt 73 may be
provided with a sliding sheet for reducing the sliding load. In
that case, a small amount of oil is supplied between the inner
surface of the heating belt 73 and the surface of the sliding sheet
via an oil supply member within the heating belt 73.
[0090] A single heating source 71pL, such as a halogen lamp, is
disposed within the tubular heating pad 71p. Alternatively, the
number of heating sources 71pL may be two or more. Furthermore,
multiple heating sources 71pL with different calorific values may
be disposed such that optimal temperature distribution is generated
in accordance with the size of the sheet P, and these heating
sources 71pL may be selectively used in accordance with the size of
the sheet P. Moreover, if the temperature differs between the
center and the edges of the sheet P in the width direction (i.e., a
direction orthogonal to the plane of FIG. 7) thereof, the heating
sources 71pL may be disposed in correspondence with the center and
the edges of the sheet P in the width direction thereof so that the
in-plane temperature of the sheet P is made uniform.
[0091] In this case, the pressing roller 72 serves as a rotational
driving source for the heating belt 73 and is disposed in a
rotatable manner in a clockwise direction R4 by a rotation driver,
such as a rotational driving motor.
[0092] Specifically, when the pressing roller 72 rotates, the sheet
P is transported downstream, and the heating belt 73 is rotated
(slave-driven) in the circumferential direction thereof (i.e., the
counterclockwise direction R2). Then, due to the rotation of the
heating belt 73, the internal heating roller 75 and the external
heating roller 76 are rotated (slave-driven).
[0093] In such a fixing device 70, the configuration related to the
control for reciprocating the heating belt 73 in the axial
direction of the internal heating roller 75 is the same as that in
the first exemplary embodiment. Therefore, the description of the
configuration will be omitted.
[0094] Although the exemplary embodiments of the present invention
have been described in detail above, the foregoing description of
the exemplary embodiments disclosed in this specification has been
provided for the purposes of illustration and description in all
aspects and is not intended to limit the exemplary embodiments of
the invention to the technologies disclosed. Specifically, the
technical scope of the exemplary embodiments of the invention
should not be interpreted limitedly based on the description of the
above exemplary embodiments but should be interpreted based on the
following claims, and includes technologies equivalent to those
within the scope of the claims and all modifications so long as
they are within the scope of the claims.
[0095] For example, although the above exemplary embodiments are
applied to an image forming apparatus of an intermediate-transfer
type that transfers toner images transferred on an intermediate
transfer belt onto a sheet, the exemplary embodiments are not to be
limited to an image forming apparatus of such a type, and may
alternatively be applied to an image forming apparatus of a
direct-transfer type that directly transfers a developer image on a
photoconductor drum (as an example of an image bearing member) onto
a sheet or the like.
[0096] Furthermore, although the above exemplary embodiments are
applied to an example for forming a color image, the exemplary
embodiments may alternatively be applied to an example for forming,
for example, a monochrome image.
[0097] Furthermore, although a sheet of paper is used as a
recording medium in the above exemplary embodiments, various kinds
of recording media on which an image can be formed, such as a film
or a postcard, may be used.
[0098] Although the above exemplary embodiments of the present
invention are applied to a color printer, the exemplary embodiments
may alternatively be applied to other kinds of image forming
apparatuses, such as a color copier, a facsimile apparatus, or an
image forming apparatus having both copying and facsimile
functions.
* * * * *